Brief introduction to the causes of the water ingress of the cable and the countermeasures Description After the cable enters the water, under the action of the electric field, water tree aging will occur, and finally lead to cable breakdown. Water trees are collections of voids filled with water ranging from 0.1m to several microns in diameter. A local high electric field site formed by impurities, pores, and insulation in the insulation and the joint surface of the inner and outer semiconductive layers is the starting point of occurrence of the water tree. The development process of water trees is generally more than 8 years. The higher the humidity, temperature, and voltage, the more ions in the water, the faster water trees will develop.
Causes 1. The newly purchased tube-forming cables are sealed with plastic sealing sleeves at both ends. However, after a period of use, the remaining ones are wrapped in plastic paper and the outside is tied with a rope. The seal is not good. Water vapor will infiltrate the cable.
2. When the cable is laid during cable laying, the cable head wrapped with plastic paper may sometimes be immersed in water to allow the water to enter the cable. When the cable is towed and worn, the outer jacket may sometimes be cracked.
3. After being laid, the cable heads are not manufactured in time, so that the unsealed cable ports are exposed to the air for a long period of time, or even immersed in water, so that a large amount of moisture enters the cable.
4. When the cable head is manufactured, when the cable head is manufactured (including the terminal head and the intermediate connector), due to the intention of the production personnel, the cable end sometimes slides into the cable well with water.
5. When the cable is running, when the breakdown of the intermediate connector breaks down, the water in the cable well will enter the cable along the gap. At the construction site, external cables will cause the cable to break or break down, and the cable will also enter the water.
Solution The drying process after the cable is filled with water is very difficult (for example, hot nitrogen is used for pressure drying), and the corresponding equipment is generally not configured. In actual operation, if the cable R6 enters the water, we only saw off the front several meters. If the entire cable has been flooded, we would not be able to make it. Therefore, the prevention of cable flooding should be based on prevention. The following measures should be taken: 1. The cable head should be sealed off the sawn cable end. Whether it is stacked or laid, it must be sealed with plastic (using a dedicated cable gland) Prevent moisture infiltration.
2. The cable head should be made in time after laying the wire.
3, when you purchase a cable, you must choose a manufacturer with excellent quality. Since the impurities, pores, etc., in the insulation are the starting point for the occurrence of water trees, the quality of the cable is critical to prevent the aging of the water tree.
4, to strengthen the management of the cable head manufacturing process Once the cable into the water, the first breakdown phenomenon is often the cable head, and thus the wire head is made well, you can extend the cable's overall life. For example, when the cable is peeling off the semiconductor layer, we have several vertical lines on the semiconductor layer, and then strip the semiconductor like stripping sugar cane. However, if you use a knife to draw too much, you will injure the insulating layer and give the water tree an opportunity. In addition, in the soldering process, because no power source is available, the torch is used to melt the solder directly. At this time, the flame will damage the copper shielding layer and the insulating layer. Therefore, to prevent this phenomenon, the correct method may be to configure the UPS, because the solder The time required is generally only 10 minutes and the power is not more than 500W.
5, the use of shrinkable cable head 3M company's cold-shrinkable silicone rubber cable accessories, production is simple and convenient, no torch, no solder. The silicone rubber cable attachment is elastic and tightly attached to the cable to overcome the shortcomings of the heat shrinkable material (the heat shrinkable material is not elastic, and there is a gap between the cable body and the cable body during the process of thermal expansion and contraction of the cable. Provides convenience for the development of water trees). At present, the 3M company's cold-shrinkable cable accessories are used for the intermediate joints of all major cables of our bureau.
6. The long cable uses several long cables of the cable branch box of our bureau, each length is about 3km. For this cable, in addition to the middle connector, we also use one to two cable branch boxes, once one of the cables enters After water, it will not spread to other sections of cable, but also easy to find in the cable fault segmentation 8.7/10kV grade cable used in 7 and 10kV systems The grade cable insulation thickness of 4.5mm, and 6/10kV grade cable The insulation thickness is 3.4mm. Due to the increase of cable insulation thickness, the field strength is reduced and water tree aging can be prevented. At the same time, since the l0kV neutral current system is single-phase grounded, the cable must withstand 1.73 times the phase voltage and run as required. 2h, therefore, it is necessary to thicken the cable insulation.
Causes 1. The newly purchased tube-forming cables are sealed with plastic sealing sleeves at both ends. However, after a period of use, the remaining ones are wrapped in plastic paper and the outside is tied with a rope. The seal is not good. Water vapor will infiltrate the cable.
2. When the cable is laid during cable laying, the cable head wrapped with plastic paper may sometimes be immersed in water to allow the water to enter the cable. When the cable is towed and worn, the outer jacket may sometimes be cracked.
3. After being laid, the cable heads are not manufactured in time, so that the unsealed cable ports are exposed to the air for a long period of time, or even immersed in water, so that a large amount of moisture enters the cable.
4. When the cable head is manufactured, when the cable head is manufactured (including the terminal head and the intermediate connector), due to the intention of the production personnel, the cable end sometimes slides into the cable well with water.
5. When the cable is running, when the breakdown of the intermediate connector breaks down, the water in the cable well will enter the cable along the gap. At the construction site, external cables will cause the cable to break or break down, and the cable will also enter the water.
Solution The drying process after the cable is filled with water is very difficult (for example, hot nitrogen is used for pressure drying), and the corresponding equipment is generally not configured. In actual operation, if the cable R6 enters the water, we only saw off the front several meters. If the entire cable has been flooded, we would not be able to make it. Therefore, the prevention of cable flooding should be based on prevention. The following measures should be taken: 1. The cable head should be sealed off the sawn cable end. Whether it is stacked or laid, it must be sealed with plastic (using a dedicated cable gland) Prevent moisture infiltration.
2. The cable head should be made in time after laying the wire.
3, when you purchase a cable, you must choose a manufacturer with excellent quality. Since the impurities, pores, etc., in the insulation are the starting point for the occurrence of water trees, the quality of the cable is critical to prevent the aging of the water tree.
4, to strengthen the management of the cable head manufacturing process Once the cable into the water, the first breakdown phenomenon is often the cable head, and thus the wire head is made well, you can extend the cable's overall life. For example, when the cable is peeling off the semiconductor layer, we have several vertical lines on the semiconductor layer, and then strip the semiconductor like stripping sugar cane. However, if you use a knife to draw too much, you will injure the insulating layer and give the water tree an opportunity. In addition, in the soldering process, because no power source is available, the torch is used to melt the solder directly. At this time, the flame will damage the copper shielding layer and the insulating layer. Therefore, to prevent this phenomenon, the correct method may be to configure the UPS, because the solder The time required is generally only 10 minutes and the power is not more than 500W.
5, the use of shrinkable cable head 3M company's cold-shrinkable silicone rubber cable accessories, production is simple and convenient, no torch, no solder. The silicone rubber cable attachment is elastic and tightly attached to the cable to overcome the shortcomings of the heat shrinkable material (the heat shrinkable material is not elastic, and there is a gap between the cable body and the cable body during the process of thermal expansion and contraction of the cable. Provides convenience for the development of water trees). At present, the 3M company's cold-shrinkable cable accessories are used for the intermediate joints of all major cables of our bureau.
6. The long cable uses several long cables of the cable branch box of our bureau, each length is about 3km. For this cable, in addition to the middle connector, we also use one to two cable branch boxes, once one of the cables enters After water, it will not spread to other sections of cable, but also easy to find in the cable fault segmentation 8.7/10kV grade cable used in 7 and 10kV systems The grade cable insulation thickness of 4.5mm, and 6/10kV grade cable The insulation thickness is 3.4mm. Due to the increase of cable insulation thickness, the field strength is reduced and water tree aging can be prevented. At the same time, since the l0kV neutral current system is single-phase grounded, the cable must withstand 1.73 times the phase voltage and run as required. 2h, therefore, it is necessary to thicken the cable insulation.
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